1,656 research outputs found
Globular Cluster Distance Determinations
The present status of the distance scale to Galactic globular clusters is
reviewed. Six distance determination techniques which are deemed to be most
reliable are discussed in depth. These different techniques are used to
calibrate the absolute magnitude of the RR Lyrae stars. The various
calibrations fall into three groups. Main sequence fitting using Hipparcos
parallaxes, theoretical HB models and the RR Lyrae in the LMC all favor a
bright calibration, implying a `long' globular cluster distance scale. White
dwarf fitting and the astrometric distances yield a somewhat fainter RR Lyrae
calibration, while the statistical parallax solution yields faint RR Lyrae
stars implying a `short' distance scale to globular clusters. Various secondary
distance indicators discussed all favor the long distance scale. The `long' and
`short' distance scales differ by (0.31+/-0.16) mag. Averaging together all of
the different distance determinations yields Mv(RR) = (0.23+/-0.04)([Fe/H] +
1.6) + (0.56+/-0.12) mag.Comment: Invited review article to appear in: `Post-Hipparcos Cosmic Candles',
A. Heck & F. Caputo (Eds), Kluwer Academic Publ., Dordrecht, in pres
Distances and ages of globular clusters using Hipparcos parallaxes of local subdwarfs
We discuss the impact of Population II and Globular Cluster (GCs) stars on
the derivation of the age of the Universe, and on the study of the formation
and early evolution of galaxies, our own in particular. The long-standing
problem of the actual distance scale to Population II stars and GCs is
addressed, and a variety of different methods commonly used to derive distances
to Population II stars are briefly reviewed. Emphasis is given to the
discussion of distances and ages for GCs derived using Hipparcos parallaxes of
local subdwarfs. Results obtained by different authors are slightly different,
depending on different assumptions about metallicity scale, reddenings, and
corrections for undetected binaries. These and other uncertainties present in
the method are discussed. Finally, we outline progress expected in the near
future.Comment: Invited review article to appear in: `Post-Hipparcos Cosmic Candles',
A. Heck & F. Caputo (Eds), Kluwer Academic Publ., Dordrecht, in press. 22
pages including 3 tables and 2 postscript figures, uses Kluwer's crckapb.sty
LaTeX style file, enclose
Atmospheric Evolution
Earth's atmosphere has evolved as volatile species cycle between the
atmosphere, ocean, biomass and the solid Earth. The geochemical, biological and
astrophysical processes that control atmospheric evolution are reviewed from an
"Earth Systems" perspective, with a view not only to understanding the history
of Earth, but also to generalizing to other solar system planets and
exoplanets.Comment: 34 pages, 3 figures, 2 tables. Accepted as a chapter in
"Encyclopaedia of Geochemistry", Editor Bill White, Springer-Nature, 201
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Assessing fossil fuel COâ‚‚ emissions in California using atmospheric observations and models
Analysis systems incorporating atmospheric observations could provide a powerful tool for validating fossil fuel CO2 (ffCO2) emissions reported for individual regions, provided that fossil fuel sources can be separated from other CO2 sources or sinks and atmospheric transport can be accurately accounted for. We quantified ffCO2 by measuring radiocarbon (14C) in CO2, an accurate fossil-carbon tracer, at nine observation sites in California for three months in 2014–15. There is strong agreement between the measurements and ffCO2 simulated using a high-resolution atmospheric model and a spatiotemporally-resolved fossil fuel flux estimate. Inverse estimates of total in-state ffCO2 emissions are consistent with the California Air Resources Board's reported ffCO2 emissions, providing tentative validation of California's reported ffCO2 emissions in 2014–15. Continuing this prototype analysis system could provide critical independent evaluation of reported ffCO2 emissions and emissions reductions in California, and the system could be expanded to other, more data-poor regions
The Distances of the Magellanic Clouds
The present status of our knowledge of the distances to the Magellanic Clouds
is evaluated from a post-Hipparcos perspective. After a brief summary of the
effects of structure, reddening, age and metallicity, the primary distance
indicators for the Large Magellanic Cloud are reviewed: The SN 1987A ring,
Cepheids, RR Lyraes, Mira variables, and Eclipsing Binaries. Distances derived
via these methods are weighted and combined to produce final "best" estimates
for the Magellanic Clouds distance moduli.Comment: Invited review article to appear in ``Post Hipparcos Cosmic
Candles'', F. Caputo & A. Heck (Eds.), Kluwer Academic Publ., Dordrecht, in
pres
PACE - The first placebo controlled trial of paracetamol for acute low back pain: design of a randomised controlled trial
<p>Abstract</p> <p>Background</p> <p>Clinical practice guidelines recommend that the initial treatment of acute low back pain (LBP) should consist of advice to stay active and regular simple analgesics such as paracetamol 4 g daily. Despite this recommendation in all international LBP guidelines there are no placebo controlled trials assessing the efficacy of paracetamol for LBP at any dose or dose regimen. This study aims to determine whether 4 g of paracetamol daily (in divided doses) results in a more rapid recovery from acute LBP than placebo. A secondary aim is to determine if ingesting paracetamol in a time-contingent manner is more effective than paracetamol taken when required (PRN) for recovery from acute LBP.</p> <p>Methods/Design</p> <p>The study is a randomised double dummy placebo controlled trial. 1650 care seeking people with significant acute LBP will be recruited. All participants will receive advice to stay active and will be randomised to 1 of 3 treatment groups: time-contingent paracetamol dose regimen (plus placebo PRN paracetamol), PRN paracetamol (plus placebo time-contingent paracetamol) or a double placebo study arm. The primary outcome will be time (days) to recovery from pain recorded in a daily pain diary. Other outcomes will be pain intensity, disability, function, global perceived effect and sleep quality, captured at baseline and at weeks 1, 2, 4 and 12 by an assessor blind to treatment allocation. An economic analysis will be conducted to determine the cost-effectiveness of treatment from the health sector and societal perspectives.</p> <p>Discussion</p> <p>The successful completion of the trial will provide the first high quality evidence on the effectiveness of the use of paracetamol, a guideline endorsed treatment for acute LBP.</p> <p>Trail registration</p> <p>ACTRN12609000966291.</p
The RR Lyrae Distance Scale
We review seven methods of measuring the absolute magnitude M_V of RR Lyrae
stars in light of the Hipparcos mission and other recent developments. We focus
on identifying possible systematic errors and rank the methods by relative
immunity to such errors. For the three most robust methods, statistical
parallax, trigonometric parallax, and cluster kinematics, we find M_V (at
[Fe/H] = -1.6) of 0.77 +/- 0.13, 0.71 +/- 0.15, 0.67 +/- 0.10. These methods
cluster consistently around 0.71 +/- 0.07. We find that Baade-Wesselink and
theoretical models both yield a broad range of possible values (0.45-0.70 and
0.45-0.65) due to systematic uncertainties in the temperature scale and input
physics. Main-sequence fitting gives a much brighter M_V = 0.45 +/- 0.04 but
this may be due to a difference in the metallicity scales of the cluster giants
and the calibrating subdwarfs. White-dwarf cooling-sequence fitting gives 0.67
+/- 0.13 and is potentially very robust, but at present is too new to be fully
tested for systematics. If the three most robust methods are combined with
Walker's mean measurement for 6 LMC clusters, V_{0,LMC} = 18.98 +/- 0.03 at
[Fe/H] = -1.9, then mu_{LMC} = 18.33 +/- 0.08.Comment: Invited review article to appear in: `Post-Hipparcos Cosmic Candles',
A. Heck & F. Caputo (Eds), Kluwer Academic Publ., Dordrecht, in press. 21
pages including 1 table; uses Kluwer's crckapb.sty LaTeX style file, enclose
Spatial variation and hot-spots of district level diarrhea incidences in Ghana: 2010–2014
Background: Diarrhea is a public health menace, especially in developing countries. Knowledge of the biological and anthropogenic characteristics is abundant. However, little is known about its spatial patterns especially in developing countries like Ghana. This study aims to map and explore the spatial variation and hot-spots of district level diarrhea incidences in Ghana. Methods: Data on district level incidences of diarrhea from 2010 to 2014 were compiled together with population data. We mapped the relative risks using empirical Bayesian smoothing. The spatial scan statistics was used to detect and map spatial and space-Time clusters. Logistic regression was used to explore the relationship between space-Time clustering and urbanization strata, i.e. rural, peri-urban, and urban districts. Results: We observed substantial variation in the spatial distribution of the relative risk. There was evidence of significant spatial clusters with most of the excess incidences being long-Term with only a few being emerging clusters. Space-Time clustering was found to be more likely to occur in peri-urban districts than in rural and urban districts. Conclusion: This study has revealed that the excess incidences of diarrhea is spatially clustered with peri-urban districts showing the greatest risk of space-Time clustering. More attention should therefore be paid to diarrhea in peri-urban districts. These findings also prompt public health officials to integrate disease mapping and cluster analyses in developing location specific interventions for reducing diarrhea
The contribution of microlensing surveys to the distance scale
In the early nineties several teams started large scale systematic surveys of
the Magellanic Clouds and the Galactic Bulge to search for microlensing
effects. As a by product, these groups have created enormous time-series
databases of photometric measurements of stars with a temporal sampling
duration and accuracy which are unprecedented. They provide the opportunity to
test the accuracy of primary distance indicators, such as Cepheids, RRLyrae
stars, the detached eclipsing binaries, or the luminosity of the red clump. We
will review the contribution of the microlensing surveys to the understanding
of the physics of the primary distance indicators, recent differential studies
and direct distance determinations to the Magellanic Clouds and the Galactic
Bulge.Comment: Invited review article to appear in: `Post-Hipparcos Cosmic Candles',
A. Heck & F. Caputo (Eds), Kluwer Academic Publ., Dordrecht, in press. 21
pages; uses Kluwer's crckapb.sty LaTeX style file, enclose
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